2-25 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \Delta x &= 20.0\ut{m}\\ v_0&=70.0\ut{km/h}=\cfrac{175}{9}\ut{m/s}\\ t&=1.20\ut{s} \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} S&=v_0t+\frac{1}{2}at^2,\\ 20&=\(\frac{175}{9}\)(1.20)+\frac{1}{2}a(1.20)^2 \end{aligned} $$ $$ \begin{aligned} a&=-\frac{125}{27}\ut{m/s^2}\\ \Ans&=\abs{a}=\frac{125}{27}\ut{m/s^2}\\ &\approx4.62962962962963\ut{m/s^2}\\ &\approx4.63\ut{m/s^2}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} S&=\frac{1}{2}(v+v_0)t,\\ 20&=\frac{1}{2}\(v+\frac{175}{9}\)(1.2)\\ \end{aligned} $$ $$ \begin{aligned} v&=\frac{125}{9}\ut{m/s}\\ &\approx13.88888888888889\ut{m/s}\\ &\approx13.9\ut{m/s}\\ \end{aligned} $$